Common-mode voltage AD9283-100

Greetings! I have what is probably a dumb question but I want to be sure. The datasheet for the AD9283 says the inputs are biased to 0.3*Vdd (approx 1 volt). I also see that there is a range of +/- 200mv. I plan on driving this ADC with AD8138 (single-to-differential amplifier). It has the ability to add a common-mode voltage to the differential output. What CM would make the ADC happiest (operating under least distortion)? Exactly 0.3*Vdd? My reading of the datasheet is to stay within 200mv (up or down) from 0.3*Vdd. If so, then I will bias the AD8183 to the same (approx) 1 volt. Could the Vrefout from the AD9283 be used as the CM voltage of the AD8138? Thanks in advance!

  • 0
    •  Analog Employees 
    on Mar 11, 2019 3:08 PM

    Hi,

    The AD9283 will perform best with Analog Input Common Mode biased at 0.9V, or 0.3*Vdd for a nominal 3.0V supply. For DC coupled applications you will also want to bias the VOCM on the ADC Driver Amp to 0.9V to match the ADC Ain CM. Many newer ADC's provide a dedicated VCM output for this purpose. The older AD9283 does not. The VCM output is separate from the VREF In/Out. VREF sets the Ain Full Scale Span. The VREF output on the AD9283 should not be used to bias the Analog Input Common Mode. VREF is 1.2V-1.3V (1.25V optimal) and VCM needs to be operated from 0.7V-1.1V (0.9V optimal).

    Best Regards,

    TonyM